Welding timer



1941- 0. EISENSCHMID 2,253,370

' WELDING TIMER Filed Dec. 17, 1938 g E E l WITNESSES: me. INVENTOR W Offo Lifenschm 1'0.

%, z (Q BY ATTORNE Patented Aug. 19, 1941 WELDING TIMER Otto Eisenschmid, Berlin- Siemensstadt, Germany,

assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 17, 1938, Serial No. 246,403 In Germany March 5, 1938 Claims.

The invention relates to a short time circuit breaker through which a consumer is connected to an alternating current network for a predetermined number of alternating current periods.

As switch, discharge paths preferably grid controlled mercury vapor discharge paths with are like discharge, serve. For the purpose of determining the time during which the discharge paths are conductive, an alternating current potential which is derived from the feeding alternating current network may be used in the grid circuit and to this may be added the potential of a condenser which is gradually charged from the first energization of the discharge paths. The potential of the condenser is opposite in polarity to the alternating potential and counteracts the ignition effect of the alternating potential as soon as the condenser is sufiiciently charged.

The short-time circuit breaker of the type just described is often used for resistance spot welding and the invention is an outgrowth of this specific use of the circuit breaker. In experimenting with the circuit breaker in welding,

I found that the spot welds'produced were not of uniform quality. At numerous points, the

material to be welded was oxidized rather than fused and this indicated that at times an excess of current is supplied. However, the oxidized points were in no way uniformly spaced and they seemed to have occurred at random.

The invention arises from the realization of the principal cause of the imperfect weld. The circuit breakers with which I experimented were in general of the follow-up type. In such breakers, one of a pair of. anti-parallel connected Valves is rendered conductive by the operation of external control means and the other valve is rendered conductive in response to the current flow through the first valve and the load. The timing condenser is associated with the external control means and it is charged by a potential derived from the load as it conducts current. The timing condenser potential counteracts the potential supplied by the external control means to render the first valve conductive.

An analysis of this system and its operation revealed that the overheating of the spot welds was caused by the leakage discharge of the condenser. The overheated spots occur at irregular intervals to a certain extent because the manual circuit controller is held down too lon after the welding operation is completed. However, this would not account for highly irregular occurrence as the manual controller is, in general, held down too long. The basic cause of the irregularity resides in the fact that the overheating depends on the instant at which the condenser potential attains the value necessary to maintain the first valve non-conductive.

If the value is attained just at or near the instant in the half period when the first valve is to be rendered non-conductive, the latter is not rendered conductive and, no current flows through the load and no additional charge of the same polarity is supplied to the condenser. The charge which has been suppliedto the condenser leaks oiT and its potential at once falls to a value just below the value necessary to maintain the valve non-conductive. If the manual controller is still closed, a period later, the first valve is rendered conductive and a whole cycle of current is supplied to the material.

If the deenergizing potential is attained by the condenser just after the first valve has been rendered conductive, current continues to flow through the material for substantially a whole cycle after the condenser attains the deenergizing potential and the potential increases well above the necessary value. In such a case the leakage, which is always a slow process, does not result in an additional current impulse through the material. It is seen, therefore, that the overheated welds occur at irregular intervals depending on the phase point on the waves of the source at which the condenser potential attains the deenergizing value.

The subject matter of the invention is an improvement on such short-time circuit breakers which consists in charging the condenser, which supplies a counter potential in the grid circuit increasing with time, from two different current sources. One charge the condenser obtains through a transformer which is dependent on the consumer potential and accordingly only carries potential when the consumer is connected in through the discharge paths. The second charge the condenser obtains from a transformer which is connected directly to the feeding alternating network. The first-named charge determines in the already known manner the time of the connecting in of the discharge paths. The second charge provides for preventing the condenser from losing its potential after the switch ing process is terminated. The discharge vessel should not ignite even if the control switch is maintained closed for a substantial time. The auxiliary charge of the condenser used in accordance with the invention covers the discharge losses of the condenser which arise by reason of incomplete insulation. The rate at which the compensating potential is appied to the condenser should be sufficiently large to counteract the leakage discharge so that, even in spite of the leakage, the condenser potential remains above the deenergizing value once it is attained.

According to a further aspect of the inventive concept, one and the same rectifier serves to charge the condenser from the two dilferent alternating current sources. may, in accordance with the invention, additionally supply the negative blocking potential necessary in the grid circuit of the discharge vessel.

Further details of the invention are manifest from the exemplary embodiment of the invention illustrated in the drawing in which Figure 1 is a diagrammative View showing my invention and Figure 2 is a graph illustrating the operation of Figure 1. through anti-parallel connected hot cathode discharge vessels 2 and 3 with mercury vapor filling and grid control, to an alternating current network 24. The time of connection of the two discharge vessels 2 and 3 depends only on the potential in the grid circuit of the discharge vessel 2. The discharge vessel 3 is at any time ignited by a following control-which is to be described below in more detailafter the arc of the discharge vessel 2 is extinguished. The ignition time-point of the discharge Vessel 2 is determined by a transformer 4 which produces on an impedance 5 an alternating potential, the phase position of which is determined by the auxiliary impedance 6. The transformer 4 may, in this connection, be

so constructed that it supplies a potential with an essentially peaked wave form. The potential on impedance (resistor) 5 counteracts a negative blocking potential which is produced on the terminals of a condenser E by charging this condenserthrough a rectifier 8 and a transformer 9 from the alternating current network 2 3-. Parallel to the condenser 'l, two impedances (resisters) 22 and iii are connected and they are so dimensioned that the larger portion of the total potential of the condenser i appears on impedance it. The potentials may have the ratio 1:5 and, in such a case, of a total potential of 250 volts on condenser E, 50 volts exist on impedance 22 and 200 volts on impedance id. The complete blocking potential of condenser E is in series with the potential of impedance 5 on the control grid of the discharge vessel 2 as long as an auxiliary switch I l maintains the indicated position; since the switch arm [H of this switch connects the r condenser E or the impedance l5 directly with the impedance 5 and through the latter with the control grid of the discharge vessel 2. The auxiliary switch H is connected in through a control contact l2, for example, a foot switch on the welding machine which initiates the switching process.

A second switch arm 5 E2 of the auxiliary switch H short circuits a condenser it through an impedance I5. The condenser 64 is, therefore, discharged as long as the auxiliary switch maintains the indicated position. The condenser It supplies in the grid circuit of the discharge vessel 2 the potential which counteracts the ignition potential of transformer after the first connecting in of the discharge vessel 2. The charging of the condenser iii starts at the instant at which the two switching arms Ill and H2 of the auxiliary switch H are moved to the open position; because at this instant, condenser M is The same rectifier A welding transformer l is connected,

iii)

connected to the secondary winding of transformer l8 from which the potential of the consumer, accordingly on the welding transformer l, is derived. The alternating potential supplied by the transformer 15 is rectified by the rectifier 6 and the time of charging depends on the regulable impedance (resistance) 2?. --imultaneously, the condenser M is, however, also charged from the transformer 5? directly from the alternating current network The latter charging circuit extends from the secondary winding of transformer 9 through the rectifier 3, the impedance 22, the condenser Hi, the impedance (resistance) l8 and back to the secondary winding of transformer 9. The impedance I? is here dimensioned so large that the charg'ng current derived from transformer i3 is comparatively small. It is precisely so large that the condenser I i for some time maintains the charge which it has received through the transformer it of the consumer, even if the discharge vessels 2 and 3 and with them the consumer i are disconnected. Only when the control switch i2 is opened and thereby the auxiliary switch I I has moved its two switching arms Hi and H2 again to the closed position, the condenser l4 discharges through the impedance iii. In this case, however, no ignition of the discharge vessel 2 can any longer take place because the complete blocking potential of condenser is connected in the grid circuit of the discharge vessel 2 through the switch arm I H.

In Fig. 2, the relationship between the potentials impressed on the condenser H3 is shown. Potential is plotted vertically and time horizontally. The lowest light curve 2530 represents the potential impressed on condenser Hi from transformer ii. The upper light curve 282 represents the potential impressed on condenser l4 from transformer 65. The heavy curve 2&4 represents the sum of the two potentials. Ihe horizontal line 2% repr sents the critical potential which the potential on condenser i4 exceeds when the valves 2 and 3 are nonconductive. At point 268, the sum curve 224 crosses the critical line 2% and it may happen that, at or in the vicinity of the time instant represented by the point, the valves 2 and 3 are rendered non-conductive. Assuming that the valves are rendered non-conductive at the time corresponding to point 288 (which is the most undesirable condition) the leakage discharge from the condenser causes the potential impressed from transformers It to follow the light broken curve 253 and the sum potential would follow the heavy broken curve M2 were it not for the compensating effect represented by curve 259. The effect of the compensating potential is to raise the sum potential above the critical value as represented by the heavy curve 2H! above the critical line 206. It is seen that the rate of rise of the potential impressed on condenser M from transformer 9 must be such as to raise the sum potential above the critical value or at least leave it at this value.

It has already been mentioned that only the discharge vessel 2 is controlled in dependence upon time while the ignition of the second discharge vessel 3 depends on the current conduction of the discharge vessel 2. For this, there act in the grid circuit of the discharge vessel 3, two potentials. One of these potentials is derived from the alternating current network 24 through a transformer 9 and is supplied to an impedance (resistance) It. It is rectified through the grid cathode discharge path of the discharge vessel 3 and supplies a negative blocking potential. The condenser 20 connected in series with this potential, provides that this potential shall, for a substantial time, maintain the same value. The second potential is supplied to an impedance (resistance) 2| in the grid circuit of the discharge vessel 3 from the consumer I through the transformer I6. This potential can only arise if the consumer I is connected through the discharge vessel 2 to the alternating current network 24. The potential on impedance 2| counteracts the potential on impedance l9 and ignites discharge vessel 3 in the instant in which the current in the discharge vessel 2 passes through zero. Because of the phase lag of the current in the consumer I with reference to the potential of the alternating current network, this.,current zero passage lies at the time point at which the potential on the discharge path 3 has already assumed a positive value. At the same time point, however, there disappears the potential on consumer l and correspondingly also the potential on transformer l6 and the potential on impedance 2| may not, under certain circumstances, lead toa certain ignition of the discharge vessel 3; This difficulty is removed by connecting the capacitor 20 in series with the impedance 2!;

the capacitor maintaining its charge for some time after the zero passage of the current of the discharge vessel 2 so that the discharge vessel 3 is, with certainty, ignited directly after the discharge vessel 2.

The above-described following control often named carry-over circuit has, as compared to other circuits serving the same purpose, the advantage that it operates with simple means and requires no special auxiliary direct current potentials.

The operation of the whole circuit is as follows:

When, in spot welding, the welding transformer l is to be connected in, the switch which connects the whole circuit with the network 24 is first closedh After a certain time delay, which is necessary for the proper heating up of the hot cathode of the two discharge vessels 2 and 3, a time delay relay [3 closes its contact I3l. The control switch l2 may now be closed, thereby the two contacts Ill and N2 of the auxiliary switch H are opened. The contact H2 opens the discharge circuit of condenser I l. The contact Ill removes the connection between the control grid of the discharge vessel 2 and a negative pole of the condenser I. In the control circuit of the discharge vessel 2, there now acts only the comparatively small negative potential on impedance 22, so that the potential of transformer 4 on impedance 5 may ignite the discharge vessel 2. The welding transformer I is thereby connected in. After the connecting in of the discharge vessel 2, the discharge vessel 3 is at once also connected in in the following half wave by means of the above-explained following control I9, 20, 2|.

After the first ignition of the discharge vessel 2, the charging of condenser I4 through transformer l6 starts. As soon as the potential of condenser l4 becomes larger than the potential of transformer 4 on impedance 5, the discharge vessels 2 and 3 are no longer ignited and the switching process is finished. The time interval of this switching process depends on the regulating impedance I! in the charging circuit of capacitor l4.

If, after the end of the switching process, the control switch I2 is maintained closed, ignition of the discharge vessel 2 does not take place in spite of this because the condenser l4 holds its charge for a substantial time. Discharge losses do not prevent this because the condenser I4 is charged through the high ohmic resistance l3 from the transformer through the rectifier 8.

The described connection for the control circuit of the discharge vessel 2 is indeed of particular significance for time switching devices in which the current consumer is connected to an alternating current source through two discharge vessels in anti-parallel. It may, however, also be used when time switching devices are involved in which only a single discharge vessel serves'as circuit breaker. It is essential in each case that the condenser, which is gradually charged in dependence upon the consumer potential and thereby counteracts the ignition potential, shall be held in a charged condition after the end of the switching process by means of auxiliary charging so that no unintentional ignition of the discharge vessel shall take place after the end of the switching process. Further it is notable that both charging current circuits are supplied through one and the same rectifier.

It should further be mentioned that the following control which the ignition of discharge vessel 3 effects, in general, may be used when of two anti-parallel connected discharge vessels, only one is arbitrarily controlled, the other, on the other hand, is to be ignited in dependence upon the ignition or the switching process of the former discharge vessel. The grid circuitconnectionof the discharge vessel 3 may, accordingly, also be used when the discharge vessel 2 is ignited by other than the described means.

'I claim as my invention:

1. Device for igniting a grid control gas or vapor discharge vessel which is connected in antiparallel with another discharge vessel between an" alternating current source and a consumer, characterized by the fact that in the grid circuit of the former discharge vessel, two potential sources are connected in series, of which one is derived from said alternating current source, while the other is derived from a condenser charged by both said source and a voltage developed across said consumer.

2. For use in supplying current from a source to a load the combination comprising valve means interposed between said load and said source for controlling the flow of current, charge storing means cooperative with said valve means to interrupt the flow of current when said storing means is charged to a predetermined potential difference and so long as it is maintained at least at said potential difference, means for charging said charge storing means and functioning only until said potential difference is attained and additional means for charging said charge storing means to maintain it at least at said potential difierence after said first-named means ceases to function thereby to prevent the flow of current through said load after it has once been interrent through said load to charge. said charge storing means to said potential diiierence, and means for preventing thefiow of current to said load by reason of the leakage of said charge storing means, said preventing means including additional charging means for said charge storing means which maintains said charge storing means at least at said potential difference once said potential difference has been attained.

4. Apparatus according to claim 3 characterized by the fact that the additional charging means functions to charge said storing means during the time that said charge storing means functions and also thereafter.

5. For use in supplying a load from a source of current the combination comprising valve means interposed between said load and said source of control the flow of current from said source to said load, charge storing means cooperative with said valve means to interrupt the flow of current to said load when it is charged to a predetermined potential difference and only so long as said storing means remains charged at least to said potential diiference, means for charging said storing means and functioning only until said potential difference is attained and additional means for charging said charge storing means to maintain it at least at said potential diiTerence after said first-named charging means has ceased to function.

6. For use in supplying a load from a source of current the combination comprising valve means interposed between said load and said source to control the flow of current from said source to said load, charge storing means cooperative with said valve means to interrupt the flow of current to said load'when said storing means is charged to a predetermined potential difference and only so long as it remains charged at least to said potential difference, means responsive to the flow of current through said load for charging said storing means and functioning only until said potential difference is attained and additional means for charging said charge storing means to maintain it at least at said potential diiference in spite of the inherent leakage of said storing means after said first-named charging means has ceased to function.

'7. For use in supplying a load from a source of current the combination comprising an electric discharge device having a control electrode and a plurality of principal electrodes interposed between said load and said source for controlling the flow of current from said source to said load, means for impressing a first potential on said control electrode to maintain said device non-conductive, charge storing means connected to said control electrode, means for impressing a second potential on said control electrode, said second potential counteracting said first potential and rendering said device conductive, means responsive to the flow of current through said device for charging said storage means to a potential such as to counteract the effect of said second potential and render said valve nonconductive after it has been conductive and means for maintaining said storing means at said potential after it has been charged thereto in spite of the inherent leakage of said storing means.

8. In a time switching device, particularly for controlling the flow of current from the supply terminals of an alternating current network to a consumer through a circuit-interrupter comprising a gas discharge vessel having a control circuit, a condenser charged by current derived through a rectifier-path from the terminal voltage of said consumer for impressing a bias potential on said control circuit, and means embodying a second rectifier-path energized from the terminals of said network to supply a charging current to said condenser.

9. Device according to claim 8, characterized by the fact that the two rectifier-paths are the components of a double-anode single-cathode rectifier,

10. Device, according to claim 8, characterized by the fact that the second rectifier-path supplies a substantially constant bias potential to said control circuit.

OTTO EISENSCHMID. 

